Frequency nonlinearity calibration in frequency-modulated continuous wave radar

ABSTRACT

Various embodiments include methods and systems having a frequency-modulated continuous wave radar operable to compensate a return signal for nonlinearity in the associated radar signal that is transmitted. The radar signal can be mixed with a delayed version of the radar signal such that the mixed signal can be used to generate an estimate of the nonlinearity. The estimate can be used to compensate the return signal from an object that reflects the associated transmitted radar signal. Additional apparatus, systems, and methods can be implemented in a variety of applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/493,751, filed on Apr. 21, 2017, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present disclosure is related to sensing technologies, inparticular, to radar-based sensing technologies.

BACKGROUND

A radar system transmits a signal and receives its echo. By processingthe echo signal, the radar system is able to detect objects, and toestimate the distances, velocities, and directions associated with theobjects. Historically, a pulsed radar is used in military applications,where targets of interest are typically far away from the radar system.The pulsed radar emits short pulses, and in the silent period receivesthe echo signals. The transmitter of the pulsed radar system is turnedoff before the measurement starts. However, in many civilianapplications, such as automotive radar, wireless gesture recognition,vital sign monitoring, and other monitoring implementations, the objectsof interest are usually close to the radar. Due to the shortround-trip-delay (RTD) of the desired reflection signal, a pulsed radardoesn't work as well at close range. Instead of a pulsed radar, afrequency-modulated continuous wave or waveform (FMCW) radar is used forshort distances.

In FMCW radar, the transmission signal is modulated in frequency (or inphase) and differences in phase or frequency between the transmittedsignal and a received signal are used to measure distance to the objectfrom which the transmitted signal is reflected. A linear frequencymodulated (LFM) waveform can be used, whose instantaneous frequencylinearly increases or decreases over time. With the change in frequencybeing linear over a wide range, then the distance can be determined by afrequency comparison, with the frequency difference being proportionalto the distance. However, in practice, nonlinearity exists in thefrequency sweep of the transmitted waveform. This can result in severeperformance degradation.

SUMMARY

A frequency-modulated continuous wave radar system based on transmittinga radar signal having a linear instantaneous frequency includes amechanism to estimate and compensate for a nonlinearity in the linearinstantaneous frequency introduced by the waveform generator of theradar signal. Though the waveform generator is designed and constructedto operate to provide a linear sweep of frequency, such a waveformgenerator does not generate a perfectly ideal waveform. There is adifference in phase between the waveform generated as a radar signal tobe transmitted from an antenna and an ideal waveform corresponding tothe desired radar signal. This difference in phase translates to anonlinearity in the desired linear instantaneous frequency for thegenerated radar signal. Determination of an estimate of thisnonlinearity allows for the adjustment of a return radar signal toapproach that corresponding to the ideal waveform in the processing ofthe return radar signal. The return signal, which corresponds to thetransmitted radar signal, received at a receiver antenna is mixed withthe generated radar signal from the waveform generator to provide anoutput signal, which is converted to a first digital signal. A delaygenerator is coupled to the waveform generator to receive the radarsignal that is directed to the transmitter antenna of thefrequency-modulated continuous wave radar system and to provide adelayed radar signal. The delayed radar signal is mixed with thegenerated radar signal from the waveform generator to provide an outputsignal, which is converted to a second digital signal. The seconddigital signal is processed to generate an estimate of the nonlinearityintroduced to the radar signal at the waveform generator. The estimateis used to compensate the first digital signal to provide a compensateddigital signal that can be used to perform functions associated withdetection of an object.

Various examples are now described to introduce a selection of conceptsin a simplified form that are further described below in the detaileddescription. The Summary is not intended to identify key or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter.

According to one aspect of the present disclosure, a system having afrequency-modulated continuous wave radar, the system comprising: awaveform generator to generate a radar signal having an instantaneousfrequency, the instantaneous frequency being linear plus a nonlinearity;a transmitting antenna to transmit the radar signal; a receiving antennato receive a return signal from an object that reflects the transmittedradar signal; a first mixer to mix the radar signal with the returnsignal and to output a first mixer output signal; a firstanalog-to-digital converter to convert the first mixer output signal toa first digital mixer output signal; a delay generator coupled to thewaveform generator to generate a delayed radar signal; a second mixer tomix the radar signal with the delayed radar signal and to output asecond mixer output signal; a second analog-to-digital converter toconvert the second mixer output signal to a second digital mixer outputsignal; and circuitry to generate an estimate of the nonlinearity basedon the second digital mixer output signal and to compensate the firstdigital mixer output signal by use of the estimate.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides that the circuitry is arranged to generate theestimate as a function of time based on phase of the second digitalmixer output signal, center frequency of the radar signal, chirp rate ofthe radar signal, and delay of the delayed radar signal.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the circuitry is arranged to record the firstdigital mixer output signal and to resample the first digital mixeroutput signal at an adjusted time using the estimate.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the circuitry to resample includes aninterpolation of the first digital mixer output signal at sampled timesimmediately before and immediately after the adjusted time.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that a delay of the delay generator to generate adelayed radar signal is in the range from 100 picoseconds to 10nanoseconds.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the system includes a first low pass filtercoupling the first mixer to the first analog-to-digital converter and asecond low pass filter coupling the second mixer to the secondanalog-to-digital converter.

According to one aspect of the present disclosure, there is provided asystem having a frequency-modulated continuous wave radar, the systemcomprising: a waveform generator to generate a radar signal having aninstantaneous frequency, the instantaneous frequency being linear plus anonlinearity; a transmitting antenna to transmit the radar signal; areceiving antenna to receive a return signal from an object thatreflects the transmitted radar signal; a delay generator coupled to thewaveform generator to generate a delayed radar signal; a mixer coupledto the waveform generator to receive the radar signal; a switch havingan input coupled to the delay generator, an input coupled to a path tothe receiving antenna, and an output coupled to the mixer such that withthe switch operatively coupling the receiving antenna to the mixer, anoutput of the mixer provides a first mixer output signal from mixing theradar signal with the return signal, and with the switch operativelycoupling the delay generator to the mixer, an output of the mixerprovides a second mixer output signal from mixing the radar signal withthe delayed radar signal; an analog-to-digital converter coupled to themixer to convert the first mixer output signal to a first digital mixeroutput signal and to convert the second mixer output signal to a seconddigital mixer output signal; and circuitry to generate an estimate ofthe nonlinearity based on the second digital mixer output signal and tocompensate the first digital mixer output signal by use of the estimate.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides that the circuitry is arranged to generate theestimate as a function of time based on phase of the second digitalmixer output signal, center frequency of the radar signal, chirp rate ofthe radar signal, and delay of the delayed radar signal.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the circuitry is arranged to record the firstdigital mixer output signal and to resample the first digital mixeroutput signal at an adjusted time using the estimate.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the circuitry to resample includes aninterpolation of the first digital mixer output signal at sampled timesimmediately before and immediately after the adjusted time.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that a delay of the delay generator to generate adelayed radar signal is in the range from 100 picoseconds to 10nanoseconds.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the system includes a low pass filter couplingthe mixer to the analog-to-digital converter.

According to one aspect of the present disclosure, there is provided amethod of operating a frequency-modulated continuous wave radar, themethod comprising: generating, using a waveform generator, a radarsignal having an instantaneous frequency, the instantaneous frequencybeing linear plus a nonlinearity; transmitting the radar signal from atransmitting antenna; receiving, at a receiving antenna, a return signalfrom an object that reflects the transmitted radar signal; mixing theradar signal with the return signal and outputting a first mixer outputsignal; converting the first mixer output signal to a first digitalmixer output signal; generating, using a delay generator, a delayedradar signal from the radar signal; mixing the radar signal with thedelayed radar signal and outputting a second mixer output signal;converting the second mixer output signal to a second digital mixeroutput signal; and generating an estimate of the nonlinearity based onthe second digital mixer output signal and compensating the firstdigital mixer output signal by use of the estimate.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides that generating the estimate of the nonlinearityincludes estimating the nonlinearity as a function of time based onphase of the second digital mixer output signal, center frequency of theradar signal, chirp rate of the radar signal, and delay of the delayedradar signal.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that compensating the first digital mixer outputsignal includes recording the first digital mixer output signal andresampling the first digital mixer output signal at an adjusted timeusing the estimate.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that resampling the first digital mixer outputsignal includes an interpolating the first digital mixer output signalat sampled times immediately before and immediately after the adjustedtime.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the method includes operating a switch with amixer that provides the first mixer output signal and the second mixeroutput signal in a calibration mode or in a compensation mode such thatthe calibration mode is executed with the switch operatively couplingthe delay generator to the mixer, and the compensation mode is executedwith the switch operatively coupling the mixer to the receiving antenna

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the method includes applying a fast Fouriertransform to compensated first digital mixer output signal to detect theobject and to estimate a delay associated with transmitting the radarsignal and receiving the return signal.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the method includes using the compensated firstdigital mixer output signal to determining one or more from a setincluding distance, velocity, and direction associated with the object.

Optionally, in any of the preceding aspects, a further implementation ofthe aspect provides that the method includes operating thefrequency-modulated continuous wave radar in an automobile or a terminaldevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a comparison of an ideal frequency over time relationship fora transmitted waveform compared with a frequency over time relationshipin a non-ideal system, according to an example embodiment.

FIG. 2 is a block diagram of an example system including afrequency-modulated continuous wave radar, according to an exampleembodiment.

FIG. 3A illustrates an example nonlinearity estimation section of theexample system of FIG. 2, according to an example embodiment.

FIG. 3B illustrates an example nonlinearity compensation section ofexample the system of FIG. 2, according to an example embodiment.

FIG. 3C is a block diagram of an example resampling implementation in anonlinearity compensator such as the nonlinearity compensator of FIGS.2, 3A, and 3B, according to an example embodiment.

FIGS. 4A-4D illustrate sequencing of the compensation of a receivedsignal associated with FIGS. 3A-3B from mixer output to a resampledsequence, according to an example embodiment.

FIG. 5 shows a simulation of a received signal for an ideal case, anon-ideal case, and a case with compensation, according to an exampleembodiment.

FIG. 6 shows an alternative example system similar to the system of FIG.2, according to an example embodiment.

FIG. 7 is a flow diagram of features of an example method of operating asystem having a frequency-modulated continuous wave radar, according toan example embodiment.

FIG. 8 is a block diagram of features of an example system having afrequency-modulated continuous wave radar with nonlinearity estimatorand nonlinearity compensation calibration, according to an exampleembodiment.

FIG. 9 is a block diagram of features of an example system having afrequency-modulated continuous wave radar with frequency nonlinearitycalibration of the frequency-modulated continuous wave radar, accordingto an example embodiment.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense, and the scope of thepresent invention is defined by the appended claims.

The functions or algorithms described herein may be implemented insoftware in an embodiment. The software may consist of computerexecutable instructions stored on computer readable media or computerreadable storage device such as one or more non-transitory memories orother type of hardware based storage devices, either local or networked.Further, such functions correspond to modules, which may be software,hardware, firmware or any combination thereof. Multiple functions may beperformed in one or more modules as desired, and the embodimentsdescribed are merely examples. The software may be executed on a digitalsignal processor, an application specific integrated circuit (ASIC),microprocessor, or other type of processor operating on a processingsystem, such as but not limited to a computer system, such as a personalsignal processing device, personal computer, server, or other computersystem, turning such processing system into a specifically programmedmachine.

In various embodiments, an online calibration is provided to estimateand compensate frequency sweep nonlinearity in FMCW radar. Calibrationis online in that the components for measurement, estimation, andcompensation can be integrated with systems including the FMCW radar.Such systems can include, but are not limited to, applications forautomotive radar, radar-based gesture recognition and vital signmonitoring used in smart watch and other wearable devices.

In various embodiments, a delay line (DL) technique can be used toestimate frequency sweep nonlinearity. Such techniques can includemixing a waveform that is being transmitted with a delayed version ofthe waveform, and estimating nonlinearity, associated with a receivedsignal from reflection of the transmitted waveform, via processing thesignal at a mixer output from mixing the waveform being transmitted andits delayed version. The delayed version of the waveform may include adelay in the range from 100 picoseconds to 10 nanoseconds or otherranges. Processing this mixed signal provides a calibration method thatprovides an estimate to compensate the nonlinearity in the receivedsignal to the radar system. This approach has lower computationalcomplexity and can deal with larger nonlinearity than conventionalapproaches, especially for short-range radar systems, for example,automotive radar, gesture recognition, vital side monitoring, and othermonitoring systems.

An ideal waveform for transmission in an FMCW radar can be taken to be asignal, s(t):

s(t)=e ^(j2π(f) ^(c) ^(t+0.5γt) ² ⁾,  (1)

with f_(c) and γ being the center frequency for the waveform and thechirp rate. A chirp, which can be referred to as a sweep signal, is asignal in which the frequency increases or decreases with time. Thechirp rate is the rate of change in the chirp. The instantaneousfrequency for s(t) is given as f_(c)+γt, linearly increasing over timet.

The received signal, as a reflected signal from an object to which thetransmitted signal is incident, can be modeled as x(t):

x(t)=βs(t−τ)=βe ^(j2π(f) ^(c) ^((t−τ)+0.5γ(t−τ)) ² ⁾,  (2)

with β and τ being amplitude and delay, respectively. The signals s(t)and x(t) can be combined at a mixer having output, y(t):

y(t)=x*(t)s(t)=βe ^(j2π(f) ^(c) ^(τ−0.5γτ) ² ⁾ e ^(j2πγtτ),  (3)

which is a sinusoid over t, where x*(t) is the complex conjugate ofx*(t). From applying a fast Fourier transform (FFT) to y(t), objects canbe detected, and the associated delay τ can be estimated.

However, in practical systems, the frequency is not linear. FIG. 1 is acomparison of an ideal frequency over time relationship for atransmitted waveform in curve 103 compared with a frequency over timerelationship, in a non-ideal system, in curve 113. A non-ideal waveformtransmitted in an FMCW radar, corresponding to the ideal waveform, canbe taken to be:

s(t)=e ^(j2π(f) ^(c) ^(t+0.5γt) ² ^(+ε(t))),  (4)

where ε(t) is a difference in phase between the waveform generated asthe radar signal to be transmitted from an antenna and a ideal waveformcorresponding to the radar signal, which ε(t) may be referred to as adenoting a phase error. The instantaneous frequency for s(t) is nowgiven as f_(c)+γt+ε′(t), which is not perfectly linear. The term, ε′(t),is the time derivative of ε(t) and is a nonlinearity added to the linearinstantaneous frequency, where this nonlinearity is an unwanted artifactfrom generation of the radar signal.

The received signal, as a reflected signal from an object to which thetransmitted signal is incident, for the non-ideal case, can now bemodeled as:

y(t)=βs(t−τ)=βe ^(j2π(f) ^(c) ^((t−τ)+0.5γ(t−τ)) ² ^(+ε(t−τ))).  (5)

The signals s(t) and x(t) combined at the mixer have output, y(t):

y(t)=x*(t)s(t)=βe ^(j2π(f) ^(c) ^(τ−0.5Γτ) ² ⁾ e^(j2π(γtτ+ε(t)−ε(t−τ))),  (6)

which is not a perfect sinusoid over t. Applying a fast Fouriertransform (FFT) to y(t) of the non-ideal case without calibration yieldsperformance degradation.

FIG. 2 is a block diagram of an embodiment of an example system 200including a FMCW radar. System 200 includes a waveform generator 202 togenerate a radar signal for transmission, a transmitting antenna 206 totransmit the radar signal, a receiving antenna 216 to receive a returnsignal that is a reflection of the transmitted radar signal from anobject, which can be viewed as an echo of the transmitted signal.Waveform generator 202 can be implemented using a voltage controlledoscillator (VCO). The radar signal from waveform generator 202 can be aprocessed signal for transmission by transmitting antenna 206. Intypical implementations, the radar signal from waveform generator 202can be operated on by a power amplifier (PA) 204 to provide a processedradar signal to transmitting antenna 206. In a similar situation, thereceived return signal can be a processed return signal. In typicalimplementations, the return signal form receiving antenna 216 can beoperated on by a low noise amplifier 214 to provide a processed returnsignal.

System 200 can include a mixer 207 having an input coupled to waveformgenerator 202 to receive the radar signal that is generated fortransmission and an input coupled to a path to the receiving antenna216. Mixer 207 includes an output to provide a primary mixed signal thatcan be processed to determine distances, velocities, and directionsassociated with objects. Prior to processing to determine distances,velocities, and directions associated with the objects, the primarymixed signal can be applied to an analog-to-digital converter 212.Analog-to-digital converter (ADC) 212 can be coupled to mixer 207 by alow pass filter (LPF) 209 such that the primary mixed signal isfiltered, according to the settings of the LPF 209, and provided to ADC212.

The output of ADC 212 can be coupled to a processing module 220 tocompensate the received return signal after processing by mixer 207, LPF209, and ADC 212. Processing module 220 can include circuitry for anonlinearity compensator 224 to compensate the processed received signaland a nonlinearity estimator 225 that provides an input to nonlinearitycompensator 224. For example, after generating an estimate of ε′(t),nonlinearity estimator 225 can provide the estimate of ε′(t) tononlinearity compensator 224. Nonlinearity compensator 224 can operateon the signal that is output from ADC 212 using the estimate of ε′(t).For the data signals {y[n]} from ADC 212, nonlinearity compensator 224can generate a new set of data signals {{tilde over (y)}[n]}, where eachvalue of the new set at n is equal to a value for the output from ADC212 at a time shifted based on ε′(t). Nonlinearity compensator 224 andnonlinearity estimator 225 of processing module 220 can be implementedin an ASIC. Such an ASIC may include a processor with a limitedinstruction set. Processing module 220 can include data storage to holdsignal data being processed. Depending on the architecture of system200, processing module 220 may be realized with one or more processorsand one or more data storage devices to store instructions and holdsignal data being processed.

System 200 also includes a delay generator 215 coupled to waveformgenerator 202 to provide a delayed radar signal. The delayed radarsignal can be provided as the generated radar signal, from waveformgenerator 202 to be transmitted, delayed by a delay of the delaygenerator 215. The delay can be in the range from 100 picoseconds to 10nanoseconds. Other delay values may be used. Delay generator 215 iscoupled to an input of a mixer 217, which also has an input coupled towaveform generator 202 to receive the generated radar signal fromwaveform generator 202. Mixer 217 has an output to provide a mixeroutput signal that provides a basis for using the circuitry ofprocessing module 220 to estimate a nonlinearity in the instantaneousfrequency of the radar signal to compensate a received return signalreceived at the receiving antenna from an object that reflects thetransmitted radar signal. Processing module 220 can be coupled to mixer217 by a LPF 219 and an ADC 222. ADC 222 can be arranged with LPF 219 toprocess the mixer output signal into a digital signal to be processed byprocessing module 220.

System 200 can be viewed as having two parts: a nonlinearity estimationsection and a nonlinearity compensation section. FIG. 3A shows anembodiment of a nonlinearity estimation section 305 of example system200 of FIG. 2. In nonlinearity estimation section 305 is delay generator215, mixer 217, LPF 219, ADC 222, and nonlinearity estimator 225 ofprocessing module 220. In operation, a radar signal generated bywaveform generator 202, where the radar signal is being transmitted, isalso provided to DL 215. The generated radar signal can have aninstantaneous frequency, where the instantaneous frequency is linearplus an unwanted and unknown nonlinearity, and has a center frequencyand a chirp rate. DL 215 operatively imparts a delay to the radar signalto generate the delayed radar signal. The delay imparted by the delaygenerator to generate a delayed radar signal can be in the range from100 picoseconds to 10 nanoseconds. Other delay values may be used. DL215 can be implemented using a conventional delay generator. Examples ofdelay generator include an arrangement of an appropriate length of coaxcable, inductor-capacitor delay lines, resistor—capacitor circuits, orother delay circuit in an integrated circuit. The delay generator may bea variable delay generator that can select amounts of delay to applydifferent delays. Testing can be conducted to determine the appropriateamount of delay to impart to the generated signal.

The generated radar signal and the generated delay radar signal isprovided to mixer 217 to mix the generated radar signal with the delayedradar signal and to provide a mixer output signal, which can be given by

$\begin{matrix}\begin{matrix}{{y_{DL}(t)} = {e^{j\; 2{\pi {({{f_{c}\tau_{DL}} - {0.5{\gamma\tau}_{DL}^{2}}})}}}e^{j\; 2{\pi {({{\gamma \; t\; \tau_{DL}} + {ɛ{(t)}} - {ɛ{({t - \tau_{DL}})}}})}}}}} \\{{\approx {e^{j\; 2{\pi {({{f_{c}\tau_{DL}} - {0.5{\gamma\tau}_{DL}^{2}}})}}}e^{j\; 2{\pi {({{\gamma \; t\; \tau_{DL}} + {{ɛ^{\prime}{(t)}}\tau_{DL}}})}}}}}}\end{matrix} & (7)\end{matrix}$

where τ_(DL) is the known small delay of DL 215, and ε′(t) is the timederivative of ε(t), where ε(t) is referred to as a phase error, herein.The mixer output signal y_(DL)(t) can be applied to LPF 219, whoseoutput is provided to ADC 222. The output of ADC 222 is provided tononlinearity estimator 225 of processing module 220.

The circuitry of nonlinearity estimator 225 of processing module 220,can estimate a derivative of a phase error of the generated radar signalbased on the mixer output signal to compensate a received signalreceived at the receiving antenna from an object that reflects thetransmitted processed signal. That is, the circuitry of nonlinearityestimator 225 can generate an estimate of the nonlinearity of theinstantaneous frequency based on the digital mixer output signal fromADC 222. Nonlinearity compensator 224 can be arranged to estimate thederivative of the phase error, which is the nonlinearity of theinstantaneous frequency, as a function of time based on phase of themixer output signal, the center frequency, the chirp rate, and thedelay. From the above equation, ε′(t) can be estimated as

$\begin{matrix}{{{ɛ^{\prime}(t)} = {\frac{1}{2{\pi\tau}_{DL}}\left\lbrack {{{angle}\left( {y_{DL}(t)} \right)} - {2{\pi \left( {{f_{c}\tau_{DL}} - {0.5{\gamma\tau}_{DL}^{2}} + {\gamma \; t\; \tau_{DL}}} \right)}}} \right\rbrack}},} & (8)\end{matrix}$

where the angle (y_(DL)(t)) is the phase of the mixer output signaly_(DL)(t). The estimated derivative can be provided to nonlinearitycompensator 224 of processing module 220 to compensate the receivedreturn signal received at the receiving antenna from an object thatreflects the transmitted processed signal. The output of ADC 222 and theestimated derivative can be stored in processing module 220 according tothe discrete times of the ADC 222 for processing by the nonlinearitycompensator 224. Nonlinearity estimation section 305 may be structuredas an independent unit that can be coupled to a FMCW radar system.

FIG. 3B shows an embodiment of a nonlinearity compensation section 310of example system 200 of FIG. 2. Nonlinearity compensation section 310can include components of what may be termed a conventional FMCW radar.For example, a conventional FMCW radar may include components similar toLNA 214, mixer 207, LPF 209, and ADC 212. Nonlinearity compensationsection 310 provides a novel mechanism to compensate for nonlinearityintroduced into the generated radar signal from waveform generator 202.The circuitry of nonlinearity compensation section 310 of processingmodule 220 can apply the estimated nonlinearity (estimated derivative ofthe phase error) to compensate the processed received return signal. Thereceived return signal from the receiving antenna can be operated on byLNA 214 and processed by mixer 207. Mixer 207 can be arranged in system200 to mix the generated radar signal from waveform 202 with a form ofthe return signal received from the object that reflects the transmittedradar signal to provide a primary mixed signal. The form of the returnsignal may be the return signal received by receiving antenna 216.Typically the form of the return signal input to mixer 207 is fromprocessing by LNA 214. ADC 212 is arranged in system 200 to process theprimary mixed signal into a digital received signal as a processedreturn signal.

In a short-range radar, the delay τ associated the transmission of agenerated signal and the reception of its reflection from an object issmall. Hence, the primary mixed signal at the output of mixer 207 can begiven as

$\begin{matrix}{\begin{matrix}{{y(t)} = {\beta \; e^{j\; 2{\pi {({{f_{c}\tau} - {0.5{\gamma\tau}^{2}}})}}}e^{j\; 2{\pi {({{\gamma \; t\; \tau} + {ɛ{(t)}} - {ɛ{({t - \tau})}}})}}}}} \\{{\approx {\beta \; e^{j\; 2{\pi {({{f_{c}\tau} - {0.5{\gamma\tau}^{2}}})}}}e^{j\; 2{\pi\gamma\tau}^{\lbrack{t + \frac{ɛ^{\prime}{(t)}}{\gamma}}\rbrack}}}}}\end{matrix}.} & (9)\end{matrix}$

The primary mixed signal can be processed by LPF 209 prior to conversionto a digital signal by ADC 212, where output of the ADC 212 provides thedigital return signal to the processing module 220. The circuitry ofnonlinearity compensator 224 of processing module 220 can be arranged tooperate on the digital return signal to compensate the digital returnsignal by a resampling based on the estimated nonlinearity, provided bynonlinearity estimator 225.

FIG. 3C is a block diagram of an embodiment of an example resamplingimplementation in a nonlinearity compensator such as nonlinearitycompensator 224 of FIGS. 2, 3A, and 3B. In an example resamplingprocedure, consider original samples, as a set of raw samples {y[n]},which can be received at nonlinearity compensator 224 from ADC 212, andmay be recorded in data storage 226 in nonlinearity compensator 224 orother section of processing module 220. The original samples are givenby

y[n]=y(nΔt).  (10)

From a review of the approximate signal of equation (9), it can be seenthat the recorded data can be approximately resampled as follows:

$\begin{matrix}{{\overset{\sim}{y}\lbrack n\rbrack} = {{y\left( {{n\; \Delta \; t} - \frac{ɛ^{\prime}\left( {n\; \Delta \; t} \right)}{\gamma}} \right)} = {\beta \; e^{j\; 2{\pi {({{f_{0}\tau} - {0.5{\gamma\tau}^{2}}})}}}e^{j\; 2{\pi\gamma\tau}\; n\; \Delta \; t}}}} & (11)\end{matrix}$

to provide a compensated signal. After generating an estimate of ε′(t),nonlinearity estimator 225 can provide the estimate of ε′(t) tononlinearity compensator 224 at a number of discrete times. Nonlinearitycompensator 224 can provide ε′(t) at times nΔt to an interpolator 228 ofnonlinearity compensator 224 to generate a new set of data signals{{tilde over (y)}[n]}, where each value of the new set at n is equal toa value for the output from ADC 212 at a time shifted based on ε′(t).The time shift can be provided as nΔt−ε′(nΔt)/γ as in equation (11). Anexample of a resampling step can be implemented using an interpolationtechnique, which may be a linear interpolation. Consider the following.Let y[0], y[1], . . . , y[N−1] be the raw samples, which are sampledfrom a continuous signal y(t) at time 0, Δt, 2*Δt, . . . . (N−1)*Δt,where * is the multiplication operator. Assume that the value of thesample at time 3.7*Δt is to be determined. Using a linear interpolationtechnology, this value of the samples can be computed asy[3]*0.3+y[4]*0.7 approximately. Similarly, other samples at any timebetween 0 and (N−1)*Δt can be computed. Other interpolationtechnologies, such as cubic, spline, etc., can be used. The resamplingprocedure can result in the nonlinear term ε′(t) effectively beingcancelled such that the resampling step effectively eliminates the phaseshift due to the nonlinearity.

FIGS. 4A-4D illustrate sequencing of a compensation of a received returnsignal associated with FIGS. 3A-3B from mixer output to a resampledsequence. FIG. 4A shows output from a mixer, such as mixer 207 of FIGS.3A-3B, for the ideal case in curve 430 with respect to the non-idealcase in curve 435. FIG. 4B shows an output from an ADC, such as ADC 212of FIGS. 3A-3B, with data points 440 projected on the analog signal.FIG. 4C shows resampled data points 445 with respect to the data points440 of FIG. 4B. For times

${{n\; \Delta \; t} - \frac{ɛ^{\prime}\left( {n\; \Delta \; t} \right)}{\gamma}},{y\left( {{n\; \Delta \; t} - \frac{ɛ^{\prime}\left( {n\; \Delta \; t} \right)}{\gamma}} \right)}$

can be assigned a value from the original data interpolated from themagnitudes of the data at the sampled times immediately before andimmediately after

${n\; \Delta \; t} - {\frac{ɛ^{\prime}\left( {n\; \Delta \; t} \right)}{\gamma}.}$

This interpolation is shown in FIG. 4C. Other techniques may be used toprovide the resampled data points. FIG. 4D shows the resampled sequencewithout the original data points.

FIG. 5 shows a simulation of a received return signal for an ideal case,a non-ideal case, a case with compensation. Curve 550 is arepresentation of the ideal case, which provides an ideal waveform witha narrow main lobe and low side lobes. Curve 555 is a representation ofthe non-ideal case with nonlinearity and no calibration/compensation ofthe received signal. Curve 555 shows a wider main lobe and higher sidelobes than the ideal case of curve 550, which indicates poor detectionand estimation performance. Curve 560 is a representation of a resampledsequence, as taught herein, used to provide a corresponding analogcurve. Curve 560 shows that a system implementing the compensationtechnique, associated with FIGS. 3A-3B, can provide a performancesimilar to the ideal case reflected in curve 550.

FIG. 6 shows an alternative embodiment of an example system 600 similarto system 200 of FIG. 2, but using only one mixer 627 in combinationwith a switch 618. In addition, the number of LPFs and ADCs used can bereduced. System 600 has low complexity and can provide off-linecalibration. The off-line calibration is calibration that can beconducted while system 600 is not using its FWCW radar. This off-linecalibration in this example arrangement of system 600 is provided byswitch 618.

System 600 can include a waveform generator 602, a PA 604, and atransmitting antenna 606 in combination with receiving antenna 616. LNA614, mixer 627, LPF 629, and an ADC 632 to operate as a FMCW radar.Switch 618 has an input coupled to a delay generator 615, an inputcoupled to a path to receiving antenna 616, and output coupled to mixer627 such that with the switch operatively coupling delay generator 615to mixer 627, system 600 is arranged to operate in a calibration mode.In calibration mode, switch 618 is set to provide output of DL 615 inline with the components to provide a signal to a nonlinearity estimator625 of a processing module 620 to run a nonlinearity calibration. Withswitch 618 operatively coupling the path to receiving antenna 616 tomixer 627, system 600 is arranged to operate in a compensation mode,which can also be referred to as an operation mode. In the compensationmode, switch 618 can be set to the output of LNA 614, taking DL 615off-line, to run nonlinearity compensation.

ADC 632 can be arranged in system 600 to process the mixer output signalinto a digital received return signal as a processed received returnsignal in compensation mode and to provide the mixer output signal toestimate a nonlinearity for calibration. The mixer output provided toADC 632 can be first processed by LPF 629. ADC 632 can provide the mixeroutput signal to the nonlinearity estimator 625 of processing module 620as a digital signal to estimate a nonlinearity for calibration. ADC 632can provide the mixer output signal to the nonlinearity compensator 624of processing module 620 as a digital signal to compensate the returnsignal received at receiving antenna 616. Processing module 620 canprovide the output from ADC 632 to nonlinearity compensator 624 or tononlinearity estimator 625 depending on whether system 600 is in acompensation mode or in calibration mode, respectively. A switch inprocessing module 620 (not shown), operating in conjunction with switch618, may be used to provide the appropriate digital signals tononlinearity compensator 624 and nonlinearity estimator 625.

The circuitry of nonlinearity compensator 624 and nonlinearity estimator625 can process the data from the received return signal and calibrationdata in a manner similar or identical to operation of nonlinearitycompensator 224 and nonlinearity estimator 225 of system 200 of FIG. 2.The compensated data from system 600 or system 200 can be used in avariety of systems that use FMCW radar. Such compensating systems can beused in, but are not limited to, automotive radar, gesture recognition,vital sign monitoring, and in other radar-based applications. Forexample, compensating systems similar to or identical to compensatingsystems, as taught herein, can be used in automobiles, smart phones,smart watches, and other terminal devices.

FIG. 7 is a flow diagram of features of an embodiment of an examplemethod 700 of operating a system having a FMCW radar. At 710, a radarsignal is generated using a waveform generator. The radar signal canhave an instantaneous frequency that is linear plus a nonlinearity. Thenonlinearity may be an artifact of a linear sweep generator, used as thewaveform generator, which does not provide a perfectly linearinstantaneous frequency. At 720, the radar signal is transmit from atransmitting antenna. The radar signal may be an amplified radar signal.At 730, a return signal from an object that reflects the transmittedradar signal is received at a receiving antenna.

At 740, the radar signal is mixed with the return signal and a firstmixer output signal is output. The mixing may be performed using one ofa number of mixers or may be performed by a mixer in conjunction with aswitch such that the mixer can mix different sets of signals. At 750,the first mixer output signal is converted to a first digital mixeroutput signal. At 760, a delayed radar signal generated from the radarsignal using a delay generator. At 770, the radar signal is mixed withthe delayed radar signal and a second mixer output signal is output. At780, the second mixer output signal converted to a second digital mixeroutput signal.

At 790, an estimate of the nonlinearity is generated based on the seconddigital mixer output signal and the first digital mixer output signal iscompensated using the estimate. Generating the estimate of thenonlinearity can include estimating the nonlinearity as a function oftime based on phase of the second digital mixer output signal, centerfrequency of the radar signal, chirp rate of the radar signal, and delayof the delayed radar signal. Compensating the first digital mixer outputsignal can include recording the first digital mixer output signal andresampling the first digital mixer output signal at an adjusted timeusing the estimate. Resampling the first digital mixer output signal caninclude interpolating the first digital mixer output signal at sampledtimes immediately before and immediately after the adjusted time.

Variations of method 700 or methods similar to method 700 can include anumber of different embodiments that may or may not be combineddepending on the application of such methods and/or the architecture ofsystems in which such methods are implemented. Such methods can includeoperating a switch with a mixer that provides the first mixer outputsignal and the second mixer output signal in a calibration mode or in acompensation mode. The calibration mode can be executed with the switchoperatively coupling the delay generator to the mixer, and thecompensation mode can be executed with the switch operatively couplingthe mixer to the receiving antenna.

Variations of method 700 or methods similar to method 700 can includeapplying a fast Fourier transform to compensated first digital mixeroutput signal to detect the object and to estimate a delay associatedwith transmitting the radar signal and receiving the return signal. Suchmethods can include using the compensated first digital mixer outputsignal to determine one or more characteristics for the object from aset including distance, velocity, and direction associated with theobject. Such methods can include operating the frequency-modulatedcontinuous wave radar in an automobile or a terminal device. Method 700can be implemented in different order of executing steps of method 700and may be implemented in system 200 of FIG. 2, system 600 of FIG. 6, orsimilar systems.

FIG. 8 is a block diagram of an embodiment of an example system 800having a FMCW radar. System 800 includes a signal generator means 810having an instantaneous frequency, where the instantaneous frequency islinear plus a nonlinearity. The nonlinearity may be an artifact of alinear frequency sweep that does not provide a perfectly linearinstantaneous frequency. Signal generator means 810 provides the radarsignal to a transmitter means 820 to transmit the radar signal. Theradar signal provided to transmitter means 820 may be an amplified radarsignal. The transmitted radar signal may be reflected from an object,providing a return signal. The return signal from an object thatreflects the transmitted radar signal can be received at receiver means830.

The radar signal can be provided to a mixer means 840 from signalgenerator means 810 and the return signal can provided to mixer means840 from receiver means 830. The return signal may be provided to mixer840 as an amplified return signal. Mixer means 840 can mix the radarsignal from signal generator means 810 with the return signal from thereceiver means 830 and output a first mixer output signal. The firstmixer output signal can be provided to an analog-to-digital conversionmeans 850 to convert the first mixer output signal to a first digitalmixer output signal.

The radar signal can be provided to a delay means 860 from signalgenerator means 810, where delay means 860 generates a delayed radarsignal from the radar signal. Delay means 860 provides the delayed radarsignal to mixer means 840, where mixer means 840 mixes the radar signalform signal generator means 810 with the delayed radar signal andoutputs a second mixer output signal. Mixer means 840 may be realized asa number of mixing means or a combination of a switching means andmixing means to generate the first mixer output signal and the secondmixer output signal. The second mixer output signal can be provided toanalog-to-digital conversion means 850 to convert the second mixeroutput signal to a second digital mixer output signal. Analog-to-digitalconversion means 850 may be realized as a number of analog-to-digitalconverting means or a single analog-to-digital converting means usedwith a switching means, which switching means may be associated with themixer means or with a separate switching means. The first mixer outputsignal and the second mixer output signal may be provided by one or morelow pass filtering means.

The first digital mixer output signal and the second digital mixeroutput signal can be provided from analog-to-digital conversion means850 to an estimation and compensation means 870. Estimation andcompensation means 870 can estimate the nonlinearity in the generationof the radar signal by signal generator means 810, based on the seconddigital mixer output signal, and can compensate the first digital mixeroutput signal using the estimate. The compensated first digital mixeroutput signal can be provided by estimation and compensation means 870for further processing of the return radar signal.

FIG. 9 is a block diagram of features of an embodiment of an examplesystem 900 having a FMCW radar 901 with frequency nonlinearitycalibration of FMCW radar 901 as taught herein. FMCW radar 901 caninclude components as shown in FIGS. 2 and 6 may include featuresdiscussed with respect to FIGS. 1-8. System 900 may be integrated intoan automobile, a smart phone, a smart watch, other terminal device, andother devices that have functions including short range radarapplications.

System 900 may also include, in addition to FMCW radar 901, a number ofcomponents such as a control circuitry 930, memory module 935,communications unit 940, data processing unit 945, electronic apparatus950, peripheral devices 955, display unit(s) 960, user interface 962,and selection device(s) 964. A number of these components can berealized in a common integrated circuit. These components may bestructured in a set of integrated circuit.

Control circuitry 930 can be realized as one more ASICs. Controlcircuitry 930 may be structured to provide, among other things,adjustment to gain levels and other variable parameters of the circuitryof FMCW radar 901 and can be part of estimation and compensationcircuitry of FMCW radar 901. Depending on the architecture and designedfunctions of system 900, control circuitry 930 can be realized as one ormore processors, where such processors may operate as a single processoror a group of processors. Processors of the group of processors mayoperate independently depending on an assigned function. In controllingoperation of the components of system 900 to execute schemes associatedthe functions for which system 900 is designed, control circuitry 930can direct access of data to and from a database.

System 900 can include control circuitry 930, memory module 935, andcommunications unit 940 arranged to operate as a processing unit tocontrol management of FMCW radar 901 and to perform operations on datasignals collected by FMCW radar 901. For example, control circuitry 930,memory module 935, and communications unit 940 can be arranged todetermine one or more characteristics for an object detected by FMCWradar 901 from a set including distance, velocity, and directionassociated with the object and provide the data to display unit(s) 960,memory module 935, and/or to systems external to system 900 viacommunications unit 940. Depending on the application, communicationsunit 940 may use combinations of wired communication technologies andwireless technologies

Memory module 935 can include a database having information and otherdata such that system 900 can operate on data to perform functions ofsystem 900. Data processing unit 945 may be distributed among thecomponents of system 900 including memory module 935 and/or electronicapparatus 950.

System 900 can also include a bus 937, where bus 937 provides electricalconductivity among the components of system 900. Bus 937 may includeconductive traces in an integrated circuit in which a number ofcomponents of system 900 are located. Bus 937 may include an addressbus, a data bus, and a control bus, where each may be independentlyconfigured. Bus 937 may be realized using a number of differentcommunication mediums that allows for the distribution of components ofsystem 900. Use of bus 937 can be regulated by control circuitry 930.Bus 937 may be operable as part of a communications network to transmitand receive signals including data signals and command and controlsignals.

In various embodiments, peripheral devices 955 may include drivers toprovide voltage and/or current input to FMCW radar 901, additionalstorage memory and/or other control devices that may operate inconjunction with control circuitry 930 and/or memory module 935. Displayunit(s) 960 can be arranged with a screen display that can be used withinstructions stored in memory module 935 to implement user interface 962to manage the operation of FMCW radar 901 and/or components distributedwithin system 900. Such a user interface can be operated in conjunctionwith communications unit 940 and bus 937. Display unit(s) 960 caninclude a video screen or other structure to visually projectdata/information and images. System 900 can include a number ofselection devices 964 operable with user interface 962 to provide userinputs to operate data processing unit 945 or its equivalent. Selectiondevice(s) 964 can include a touch screen or a selecting device operablewith user interface 962 to provide user inputs to operate dataprocessing unit 945 or other components of system 900.

In various embodiments, a system can include a set of processors and aset of associated non-transitory machine-readable storage devices toperform tasks for which the system is structured. The system may includea FMCW radar that can be operated, using the set of processors alongwith instructions stored in the set of non-transitory machine-readablestorage devices, including compensating a processed return radar signalfor nonlinearity in the generation of the radar signal by a waveformgenerator, as taught herein. Such set of non-transitory machine-readablestorage devices can comprise instructions stored thereon, which, whenperformed by a machine, cause the machine to perform operations, theoperations comprising one or more features similar to or identical tofeatures of methods and techniques described with respect to method 700,variations thereof, and/or features of other methods taught herein suchas associated with FIGS. 1-9. The physical structures of suchinstructions may be operated on by one or more processors. For example,executing these physical structures can cause the machine to performoperations comprising: generating, using a waveform generator, a radarsignal having an instantaneous frequency, the instantaneous frequencybeing linear plus a nonlinearity; transmitting the radar signal from atransmitting antenna; receiving, at a receiving antenna, a return signalfrom an object that reflects the transmitted radar signal; mixing theradar signal with the return signal and outputting a first mixer outputsignal; converting the first mixer output signal to a first digitalmixer output signal; generating, using a delay generator, a delayedradar signal from the radar signal; mixing the radar signal with thedelayed radar signal and outputting a second mixer output signal;converting the second mixer output signal to a second digital mixeroutput signal; and generating an estimate of the nonlinearity based onthe second digital mixer output signal and compensating the firstdigital mixer output signal using the estimate.

A number of operations can be controlled via the set of processors andthe set of non-transitory machine-readable storage devices. Operationscan include generating the estimate of the nonlinearity to includeestimating the nonlinearity as a function of time based on phase of thesecond digital mixer output signal, center frequency of the radarsignal, chirp rate of the radar signal, and delay of the delayed radarsignal. Compensating the first digital mixer output signal can includerecording the first digital mixer output signal and resampling the firstdigital mixer output signal at an adjusted time using the estimate.Resampling the first digital mixer output signal can includeinterpolating the first digital mixer output signal at sampled timesimmediately before and immediately after the adjusted time. Operationscan include operating a switch with a mixer that provides the firstmixer output signal and the second mixer output signal in a calibrationmode or in a compensation mode such that the calibration mode isexecuted with the switch operatively coupling the delay generator to themixer, and the compensation mode is executed with the switch operativelycoupling the mixer to the receiving antenna.

Operations can include applying a fast Fourier transform to compensatedfirst digital mixer output signal to detect the object and to estimate adelay associated with transmitting the radar signal and receiving thereturn signal. Operations can include using the compensated firstdigital mixer output signal to determine one or more characteristics forthe object from a set including distance, velocity, and directionassociated with the object.

Further, a machine-readable storage device, herein, is a physical devicethat stores data represented by physical structure within the device.Such a physical device is a non-transitory device. Examples ofmachine-readable storage devices can include, but are not limited to,read only memory (ROM), random access memory (RAM), a magnetic diskstorage device, an optical storage device, a flash memory, and otherelectronic, magnetic, and/or optical memory devices. Themachine-readable device may be a machine-readable medium such as memorymodule 935 of FIG. 9. While memory module 935 is shown as a single unit,terms such as “memory,” “memory module,” “machine-readable medium.”“machine-readable device,” and similar terms should be taken to includeall forms of storage media, either in the form of a single medium (ordevice) or multiple media (or devices), in all forms. For example, suchstructures can be realized as centralized database(s), distributeddatabase(s), associated caches, and servers, one or more storagedevices, such as storage drives (including but not limited toelectronic, magnetic, and optical drives and storage mechanisms), andone or more instances of memory devices or modules (whether main memory,cache storage, either internal or external to a processor; or buffers).Terms such as “memory,” “memory module.” “machine-readable medium,” and“machine-readable device,” shall be taken to include any tangiblenon-transitory medium which is capable of storing or encoding a sequenceof instructions for execution by the machine and that cause the machineto perform any one of the methodologies taught herein. The term“non-transitory” used in reference to a “machine-readable device,”“medium,” “storage medium,” “device,” or “storage device” expresslyincludes all forms of storage drives (optical, magnetic, electrical,etc.) and all forms of memory devices (e.g., DRAM, Flash (of all storagedesigns), SRAM, MRAM, phase change, etc., as well as all otherstructures designed to store data of any type for later retrieval.

As noted, the machine-readable non-transitory media, such ascomputer-readable non-transitory media, includes all types of computerreadable media, including magnetic storage media, optical storage media,flash media and solid state storage media. It should be understood thatsoftware can be installed in and sold with a device having a FMCW radar.Alternatively the software can be obtained and loaded into the devicehaving a FMCW radar, including obtaining the software through physicalmedium or distribution system, including, for example, from a serverowned by the software creator or from a server not owned but used by thesoftware creator. The software can be stored on a server fordistribution over the Internet, for example. Execution of variousinstructions may be realized by the control circuitry of the machine toexecute one or more features similar to or identical to features ofmethods and techniques described with respect to method 700, variationsthereof, and/or features of other methods taught herein such asassociated with FIGS. 1-8. For example, the instructions can includeinstructions to operate a FMCW radar as part of other systems inaccordance with the teachings herein. Control circuitry for operation ofthe FMCW radar as part of other systems can include one or more ASICs.

Although a few embodiments have been described in detail above, othermodifications are possible. For example, the logic flows depicted in thefigures do not require the particular order shown, or sequential order,to achieve desirable results. Other steps may be provided, or steps maybe eliminated, from the described flows, and other components may beadded to, or removed from, the described systems. Other embodiments maybe within the scope of the following claims.

1. A system comprising: a waveform generator to generate a source signalfor wireless transmission from at least one antenna; receive pathcircuitry coupled to receive an ingoing radio frequency (RF) signal thatis a reflection of the source signal from an object and configured toprocess the ingoing RF signal, the receive path circuitry comprising: amixer coupled to receive the ingoing RF signal and a high frequencysignal from the waveform generator, wherein the mixer produces adownconverted mixer output signal; an analog-to-digital converter thatproduces a digital mixer output signal that is based upon the mixeroutput signal; subtraction circuitry disposed electrically between themixer and the analog-to-digital converter to subtract a leakagecancellation signal from the mixer output signal; a digital to analogconverter configured to produce the leakage cancellation signal.
 2. Thesystem of claim 1, wherein the system includes a first switch coupled toreceive the mixer output signal and coupled to the subtraction circuitryto provide the received mixer output signal to the subtractioncircuitry; and a second switch coupled to receive the leakagecancellation signal and coupled to the subtraction circuitry to providethe received leakage cancellation signal to the subtraction circuitry;the operation of the first and second switches configured to operate thesubtraction circuitry in two different modes.
 3. The system of claim 2,wherein the system includes a variable gain amplifier coupled betweenthe subtraction circuitry and the analog-to-digital converter, whereinthe variable gain amplifier comprises a fixed high-gain amplifier and afixed low-gain amplifier.
 4. The system of claim 1, wherein the systemincludes a low pass filter coupled between the mixer and the subtractioncircuitry, wherein the low pass filter filters the mixer output signal.5. The system of claim 1, wherein the system includes a low pass filtercoupled between the digital to analog converter and the subtractioncircuitry, wherein the low pass filter filters the leakage cancellationsignal.
 6. The system of claim 1, wherein components of the system arestructured to include a frequency-modulated continuous wave radar. 7.The system of claim 1, further comprising: one or more additionalreceive path circuitries identical to the receive path circuitry;wherein the receive path circuitry and the one or more additionalreceive path circuitries are structured to operate in parallel withrespect the source signal generated by the waveform generator.
 8. Thesystem of claim 1, wherein the system further comprises: the at leastone antenna being a plurality of transmitter antennas, each transmitterantenna being selective in turn for transmission of a correspondingsource signal derived from the waveform generator; a plurality ofreceiver antennas, each receiver antenna coupled to a respective onereceive path circuitry of a plurality of receive path circuitriesidentical to and including the receive path circuitry, the plurality ofreceiver antennas and their coupled respective receive path circuitriesstructured to operate in parallel.
 9. The system of claim 1, wherein thesystem further comprises: the at least one antenna being a plurality oftransmitter antennas, each transmitter antenna being selective in turnfor transmission of a corresponding source signal derived from thewaveform generator; a plurality of receiver antennas, each receiverantenna selectively coupled to the receive path circuitry for signalreception in turn such that the each receiver antenna operates with eachtransmitter as a transmitter-receiver pair at selected times.
 10. Amethod comprising: generating a source signal for wireless transmissionfrom at least one antenna; receiving an ingoing radio frequency (RF)signal that is a reflection of the source signal from an object andprocessing the ingoing RF signal, the processing comprising: mixing theingoing RF signal, producing a downconverted mixer output signal;subtracting a leakage cancellation signal from the mixer output signal;and producing a digital mixer output signal that is based upon the mixeroutput signal; converting a digital signal to an analog signal toproduce the leakage cancellation signal.